Poison gas protection



Patented Mar. 19, 1946 POISON GAS PROTECTION Majer Mendelsohn, New York,N. Y.

No Drawing. Application April 17, 1942, Serial No. 439,402

37 Claims.

This invention relates to a process for preparing substances forcounteracting or protecting against the effect of poison gases, theproduct of such process, the process of treating materials with theproduct of such process, and the product of treating such materials.

This application is a continuation in part of application, Serial No.399,562, filed June 24, 1941.

Particular reference, in regard to process and products, will be made inrelation to their application for use in defense against attack bysubstances such as the material generally known under the name, mustardgas. Although termed a gas in its name, the properties of the substanceare such that, at ordinary temperatures, it is not a gas. In fact, suchsubstance may be handled under pressure as a liquid at temperaturesslightly in excess of average, or it may be held in solution, as, forinstance, in solvents such as the chlorinated hydrocarbons. Then, whenit is used for attack, it is sprayed into the air, where it forms asuspension in the form of a cloud of fine drops.

These fine drops forming the suspension then act directly upon anysubstance with which they come into contact. Attack against the personthrough the nose or mouth may, by suitable means, be made ineffective;the danger lies in the destructive effect of the substance, as, forinstance, when drops of the mustard gas, either as the dispersedliquefied substance or its solution, come into contact with the skin ofthe body, with clothing covering the body, or with other coverings, as,for instance, for foodstuffs or the like. The substance directly actsupon the skin of the body, penetrating easily and quickly throughordinary clothing. Also, it impregnates food held in packages, or thesurfaces over which one may have to walk. When one walks over such asurface after the drops have fallen thereon, the destructive substancewill penetrate through leather or rubber soles, and attack the skin ofthe wearer.

It is an object of the invention to rovide means for barring access ofthe destructive substance to that which is to be protected, as, forinstance, through the clothing or from a floor to the skin of theperson. by destroying the substance before it can attain such access, orso chemically to change the substance that it cannot produce any of thereactions of mustard gas with that which is to be protected.

It has been found that substantially all known impermeable or relativelyimpermeable materials, when used as a means of protection against thedestructive effects of mustard gas, provide no efiective barrier topassage of the mustard gas therethrough, either by absorption of thesubstance by the material or by actual destruction of the material, theresult desired by the enemy.

It is an object of the invention to, produce a protective substancewhich may be used inthe manufacture of protective garments, coverings,or the like, to impart substantial impermeability against thedestructive substance, as, for instance, by continuing to destroy thedestructive substance during attack, as such substance may come intodirect contact with the protective substance of garment or covering sothat such destructive substance may not pass unchanged into contact withanything to be protected thereagainst.

Other objects of this invention will be set forth hereinafter, or willbe apparent from the description wherein certain embodiments forcarrying out the invention are exemplified.

The invention, however, is not intended to be restricted to anyparticular composition, or any particular proportion, or any particular,product, or any particular application of any such composition orproportion or product, or any particular process of preparation, ormethod of operation or use, or any of various details thereof, evenwhere specifically described herein, as the same may be modified invarious particulars or may be applied in many varied relations withoutdeparting from the spirit and scope of the claimed invention, of whichthe exemplifying embodiments, herein described, are intended only to beillustrative, and only for the purpose of complying with therequirements of the statutes for dis closure of an operative embodiment,but not to demonstrate all of the various modifications in which theinvention might be embodied.

The basic destructive ingredient of mustard gas is capable ofdestruction by oxidation. A proper means to effectuate such oxidationmust be capable of accomplishing the oxidation rapidly enough so thatthe destructive ingredient, before it comes into contact with that whichis to be protected thereagainst, as. for instance, the body of thewearer of a garment, will have passed through a complete chemical changeto a nondangerous substance. Such an oxidizing agent. for purposes ofthis invention, must be capable of being embodied into materials of highflexibility for use, for instance, in garments. Among such ingredientshave been found that class of compounds having chromic anhydride coupledwith an alkali oxide group, as, for instance, the chromates ordichromates of the alkali metals.

Such substances normally are solids, and thus present the problem ofmaintaining them in condition immediately to react upon the destructiveingredient. point of reaction of the destructive ingredient with theprotective substance enters as a requirement. That is, water must bemade available in such state that the effect of a reactive solution ispresent immediately as the attack by the detective substance, whetherembodied as coating or sheet, to produce the effect of a solution forthe oxidizing substance, that is, the chromate, dichromate, or the like.

Further-more, a substantially greater rapidity of oxidation has beenfound to follow when the protective substance is acid, possibly becauseof the presence of dichromate. suit, a weak acid may be used as one ofthe ingredients in making the coating. It is to be noted thatsubstantially the same composition may be utilized, whether theprotection against the mustard gas be provided in the form of a coatingupon other materials, or as a sheet, with or without other materials.Therefore, the

terms, coating and sheet" are used interchangeably herein.

It may be desired to make a garment, -embodying features of theinvention, to be resistant to moisture. The protective substance,produced, as hereinafter set forth, normally is water resistant,repelling moisture. In fact, even the drops of a suspension of mustardgas will roll off a garment embodying elements of the invention.However, if a further factor of moisture resistance is desired to be setup, the

The presence of moisture at the word, gelatin, is intendedto havesignificance not only for the usual trade material known by that name,but also other materials having substantially similar. characteristics,including albuminoids such as glue or the like, wherein such materialsare made insoluble in water by the To effect this reaction ofingredients such as the alkali chromates. The solution of gelatin inwater to make a 20% solution is the customary p'roportion by which, say20 grams, of the solid are dissolved or mixed in water, and'then wateris added until the total volume, for the weight indicated, is 100 cubiccentimeters.- Furthermore, in some cases where such. materials are takenup with water, a colloidal suspension, rather as, for instance,diethylene glycol-,various sugar derivatives, derivatives of hexahydrlcalcohols, such as sorbitol, and the like.

In order to provide an example, glycerin is considered herein. In thatrelation, the quantity of glycerin added to'the batch is determined inaccordance with a number of factors,

' of the dry gelatin has been found effective.

protective substance may include an ingredient the whole purpose ofwhich is to repel or shed water. Ingredients of this kind, useful forthe purposes stated, include compounds such as. the esters of the fattyacids, the glyceryl fatty acids, the glycol fatty acids, and the like.High efficiency for this purpose has been attained by the use ofglycerol monolaurate, glyceroldilaurate, or glyceryl monoricinoleate asan ingredient in the preparation of the protective substance.

Maintenance of a substantially constant temperature has been found to beof importance properly to effect the steps vof preparing the batch fromwhich the protective substance is obtained. Also, the batch duringmixing, and the batch after it has been mixed and up to the time ofspreading, should be maintained at a substantially constant temperature.Control of the process is best effected when the temperature of thebatch is between 55 C. and 70 C. Once the batch has been brought up to apreliminarily indicated temperature, it is to be understood, in thisconnection, that substantially little, if any, variation in thattemperature should be permitted, especially after the chromate ordichromate has been added, as hereinafter set forth.

First, in preparing the batch, gelatin is taken up in water, so thatabout 20 parts of the solid gelatin is dissolved or mixed with addedwater to make up 100 parts of solution. A temperature found highlyeffective'for the batch, during processing, is 60 C.

In this connection, it is to be noted that the After the glycerin hasbeen mixed into the batch, the batch is weakly acidified; This may beeffected by adding a weak acid such as citric acid. About 2% of suchacid, based upon the weight of the gelatin, may be added. When theprotective substance is thus in an acid state, the destruction of themustard gas will proceed at a more rapid pace, and resistance thereto,therefore, is greater.

The batch is now ready for the hardening stage. In this connection,while it is possible to produce the result by other oxidizing andhardening agents, the property of the derivatives of chromic anhydrideis specifically indicated for this purpose, and particularly where thechromic anhydride is in the form of chronlate or dichromate. The saltsof sodium and potassium have been found most desirable for the purposesof this reaction. The chromate or dichromate may be in the amount ofabout 25% of the dry weight of gelatin.

The batch remains substantially fluid for a considerable period afterthe chromate 0r dichromate has been added and so long as the batchtemperature remains substantially constant. The reaction product isagitated, and then is applied to the sheet material to be coated.Substantially any material, itself having sufficient elasticity andhaving a surface to whichthe reaction product will adhere, may be usedfor this purpose. Ma.- terials such as paper, textiles, rubber, and thelike lend themselves for this purpose. The reaction product also may bespread upon metallic tables which do not react chemically with theingredients of the protective substance, to form tlnn sheets. In eithercase, the process of spreading may involve the use of a doctor blade, orany other suitable method. For instance, a felt-covered roll mayberotated in a trough containing seed oil may be used as plasticizers.

the reaction product. Paper, textile or rubber, in sheet, strip or othersuitable form, may be passed into contact with the rotating roll.Materials to be coated may be dipped. .When the reaction product isspread to form thin sheets, those sheets, after proper thickening hasoccurred, may then be handled to provide plys.

The amount of the chromate or dichromate used is far in excess of theamount required to make gelatin insoluble'in water. Thus, fabric, paper,rubber or the like, coated with the substance prepared in this manner,will shed water and the globules of the suspension in air of the mustardgas. However, if it is desired to assure waterproof properties to agreater degree, ingredients may have beenaddedto the batch during themixing." For instance, the addition of quantities of one or more of theesters of fatty acids, or of the esters of the glycerol fatty acids, orof the esters of the glycol fatty acids will impart the waterproofingproperty to the batch as finally made ready for coating or for forming asheet, and thus, to the material which has been coated therewith, orformed therefrom. These fatty substances, in a quantity of between 20%to 30% of the weight of the dry gelatin, when added to the batch, willeffectuate the desired result in the final product. Particular instancesof esters effective for the purposes indicated are glycerol monolaurate,glycerol dilaurate, and glyceryl monoricinoleate.

Other factors of waterproofing also require consideration. For instance,a plasticizer such as glycerin, which is hygroscopic, may be replaced byone which itself is insoluble in water. Such plasticizers includephthalic acid and its salts, phosphate salts, salicylic acid, and thelike. A small amount of glycerin may still be required in these cases toassure good flexibility. In such cases, a high degree of waterproofingis attained; it is more complete than if glycerin alone were used. Inthe case of textiles, croton oil or rape These last ingredients providecomplete substitutes for glycerm.

Water, of course, is present in some form necessary to facilitate theoxidation reaction, but the exact form is not clear. The imprisonedwater, whether imprisoned during the hardening process or otherwise, is,in the case of any of these plasticizers, immediately available to makethe oxidizing reagent immediately effective upon the destructivesubstance. For instance, very effective plasticizers having theseproperties have been found in those amino compounds where from twelve tosixteen carbon atoms are present in the amino group, and where thecompound is soluble 'in water, is acidic, and is liquid.

Likewise, glycerin itself may be made substantially insoluble in water.For this purpose, by the dissimilar materials, as, for instance, paper,textile, rubber or the like. The substance, either as layer, coating, orhowever it may be used, interposes itself as a barrier to passage of thedestructive substance, as such, to react upon the par ticular thing tobe protected. The protective substance has the characteristic offlexibility, and yet imports no substantial increase in weight to aprptective garment of which it may form a part, so that such protectivegarment may be carried with ease.

For certain purposes of the invention, it may be found desirable firstto coat or impregnate a carrier material, such as textile or the like,with a solution of gelatin. Then the several ingredients may be workedinto the coated material,

with the final addition of the chromate or dichromate. Sheets of thematerial, formed by applying the protective substance to metallicplates, may be picked up and positioned between layers of differentmaterials such as rubber or the like, When a protective covering isprepared from such materials, so prepared, the seams may be closed byadhering the lapped portions of sheets by means of the plastic mass ofthe batch before it has congealed fully.

On attack by mustard gas, the fluid particles strike the protectivecovering, and are intercepted by the protective coating or ply. Thechromate or dichromate, in large excess, is maintained in reactive stateby the moisture obtained either from the imprisoned moisture, or by thehygroscopicity of an ingredient, as, for instance, of a plasticizer suchas glycerin. It may be active at a high oxidizing degree because of theacid state resulting from the presence of the citric or similar weakacid. The gas is oxidized by the chromate to the destruction of itsdangerous character, and remains as relatively harmless reactionproducts.

Many other changes could be effected in the particular composition, andin the proportions thereof, and in the particular products, and in themethod of preparation and use, and in specific details thereof,hereinbefore set forth, without substantially departing from theinvention defined in the claims, the specific description being merelyembodiments capable of illustrating certain principles of the invention.

I claim:

1. The process of preparing materials for use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing gelatin and a quantity of a hardening agent of substantiallyhigh oxidizing power and in excess over the quantity required forhardening the gelatin, and forming a thin, flexible, protective layerfrom the reacted material.

addition of blood or egg albumen to the glycerin,

the glycerin itself is made insoluble. For instance, if between 20% to25% of egg or blood albumen, based on the weight of glycerin, be addedto the glycerin, the glycerin becomes substantially insoluble.

As herein indicated, the protective substance may be applied for thepurposes of the invention as a coating upon materials such as thosenormally used in manufacturing garments; likewise, it may be prepared inthe form of a sheet which then may be built up into a protective fabricor sheet material by forming a sheath of a plurality of plys of suchsheet, or by using such sheet to form a layer with one or more plys ofother or 2. The process of preparing materials for use in obtainingprotection against attack by substances such as mustard gas, includingthe step of intermixing an aqueous solution of gelatin and a quantity ofa hardening agent of substantially high oxidizing power and in excessover the quantity of the agent required forhardening the gelatin, andforming a thin, flexible, protective layer from the reacted material.

3. The process of preparing materials for use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing a weakly acidulated aqueous solution of gelatin and aquantity of a hardening agent of substantially high oxidizing power andin excess over the quantity required for hardening the gelatin, andforming a thin, flexible, protective layer from the reacted material.

,4. The process of preparing materials for use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing, in the presence of a plasticizer, gelatin and a quantity ofa hardening agent of substantially high oxidizing'power and in excessover the quantity of the agent required for hardening the gelatin, andforming a thin, flexible, protective layer from the reacted material.

. 5. The process of preparing materials for use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing, at a temperature of about 55-70 C., gelatin and a quantityof a hardening agent in obtaining protection against attack bysubstances such as mustard gas, including the step of intermixing, inthe presence of a plasticizer and at a substantially constanttemperatureoi about 60 C., a weakly acidulated aqueous solution ofgelatin and a quantity of a hardening agent of substantially highoxidizing power and in excess over the quantity of the agent requiredfor hardening the gelatin.

8. The process of preparing materials for use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing gelatin and a quantity, in excess over the quantity requiredfor hardening the gelatin, of a salt of substantially high oxidizingpower of an alkali metal and an acid containing chromium, and forming athin, flexible, protective layer from the reacted material.

9. The process of preparing materials ior use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing gelatin and a quantity, in excess over the quantity requiredfor hardening the gelatin, of a salt of an alkali metal and an acidhaving its derivation in chromic anhydride, and forming a thin,flexible, protective layer from the reacted material. v

10. The process of preparing materials for us a thin, flexible,protective layer from the reacted in obtaining protection against attackby substances such as mustard gas, including the step of intermixinggelatin and ,a quantity, in excess over the quantity required forhardening the gelatin, of a salt of an alkali metal and dichromic acid,and forming a thin, flexible, protective layer from the reactedmaterial.

11. The process of preparing materials for use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing an aqueous solution of gelatin acidulated with citric acidand a quantity'of a hardeningagent of substantially high oxidizing powerand in excess over the quantity required for hardening the gelatin, andforming a thin,

flexible, protective layer from the reacted mastances such as mustard,g'as,including the step of intermixin in the presence of .amoisture-introducing plasticizer, gelatin-and a quantity ofa hardeningagent of substantially high oxidizing power and in excess over thequantity required for hardening the gelatin, andforming a thin,flexible, protective layer from the reacted material. 1

13. The process of preparing materials for use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing, in the presence of a plasticizer and an ester of the higherfatty acids, gelatin and a quantity of a hardening agent ofsubstantially high oxidizing power and in excess over the quantityrequired for hardening the gelatin, and forming a thin, flexibleprotective layer from the reacted material.

14. The process of preparing materials for use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing, in the presence of a substance selected from the groupconsisting of the higher fatty acid esters, gelatin and a quantity, inexcess over the quantity required for hardening the gelatin, of ahardening agent of substantially high oxidizing power, and forming athin, flexible, protective layer from the reacted material.

15. The process of preparing materials for use in obtaining protectionagainst attack by'substances such as mustard gas, including the step ofintermixing, in the presence of a plasticizer, gelatin acidulated withcitric acid and a quantity,

in excess over the quantity required for harden-- ing the gelatin, of asalt of an alkali metal and dichromic acid, and forming a thin,flexible, protective layer from the reacted material.

16. The process of preparing materials for use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing, at a. temperature of about 55- '70 C. and in the presenceof a moisture-introducing plasticizer, gelatin acidulated with citricacid and a quantity, in excess over the quantity required for hardeningthe gelatin, of a salt of an alkali metal and dichromic acid, andspreading the reaction product in a thin layer over a surface.

17. The process of preparing materials for use in obtaining-protectionagainst attack by substances such as mustard gas, including the step ofintermixing a 20% aqueous solution of gelatin and an excess over thequantity required for hardening the gelatin of a hardening agent ofsubstantially high oxidizing power, and forming material.

18. The process of preparing materials for use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing a 20% aqueous solution of gelatin and a hardening agent ofsubstantially high oxidizing power in the ratio of about one part ofhardening agent to four parts of gelatin, and forming a thin, flexible,protective layer from the reacted material.

19. The process of preparing materials for use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing a 20% aqueous solution of gelatin and a quantity of aboutone part of an alkali salt of an acid having its derivation in chromicanhydride to four parts of gelatin, and forming a thin, flexible,protective layer from the reacted material.

20. The process or preparing materials for use in obtaining protectionagainst attack by substances such as mustard gas, including the step ofintermixing, at a temperature of about 55- 70 C. and in the presence ofa plasticizer, a 20% aqueous solution of gelatin, and a quantity of ahardening agent of substantially high oxidizing power, where theplasticizer is present in the ratio of about to 40 parts of plasticizerto parts of gelatin and where about one part of hardening agent isintermixed with four parts of gelatin.

21. A thin, flexible coating for relatively thin, flexible materialssuch as paper or cloth, for use in obtaining protection against attackby substances such as mustard gas, the coating being the product ofintermixin gelatin and an excess over the quantity required forhardening the gelatin of a hardening agent of substantially highoxidizing power.

22. A thin. flexible coating for relatively thin, flexible materialssuchas paper or cloth, for use I in obtaining protection against attack bysubstances such as mustard gas, the coating being the product ofintermixing an aqueous solution of gelatin and an excess over thequantity required for hardening the gelatin of a hardening stances suchas mustard gas, the coating being,

the product of intermixing a weakly acidulated solution of gelatin andan excess over the quantity required for hardening the gelatin of ahardening agent of substantially high oxidizing power.

24 A thin, flexible coating for relatively thin, flexible materials suchas paper or cloth,'for use in obtaining protection against attack bysubstances such as mustard gas, the coating being the product ofintermixing, in the presence of a plasticizer, a weakly acidulatedsolution of gelatin and in excess over the quantity required forhardening the gelatin of a hardening agent of substantially highoxidizing power.

25. A coating for use in obtaining protection against attack bysubstances such as mustard gas, the coating being the product ofintermixing, in the presence of a plasticizer and at a temperature ofabout 55-70 0., a weakly acidulated solution of gelatin and an excessover the quantity required for hardening the gelatin of a hardeningagent of substantially high oxidizing Power.

26. A thin, flexible coating for relatively thin, flexible materials,such as paper or cloth, for use in obtaining protection against attackby substances such as mustard gas, the coating being the product ofintermixing, in the presence of a moisture-introducing plasticizer, aweakly acidulated solution of gelatin and an excess over the quantityrequired for hardening the gelatin of a salt of an alkali metal and anacid having its derivation in chromic anhydride.

27. A thin, flexible coating for relatively thin, flexible materials,such as paper or cloth, for use obtaining protection against attack bysubstances such as mustard gas, the coating being the product ofintermixing, in the presence of a moisture-introducing plasticizer suchas glycerin, an aqueous solution of gelatin acidulated with citric acidand an excess over the quantity required for hardening the gelatin of asalt of an alkali metal and dichromic acid.

28. A thin, flexible coating for relatively thin, flexible materialssuch as paper or cloth, for use in obtaining protection against attackby substances such as mustard gas, the coating being the product ofintermixing, in the presence of a moisture-introducing plasticizer andof a substance selected from the group consisting of the higher fattyacid esters, an aqueous solution. of gelatin acidulated with-citric acidand an excess over the quantity required for hardening the gelatin of asalt of an alkali metal and dichromic acid.

'29. A coating for use in obtaining protection against attack bysubstances such as mustard gas, the coating being the product ofintermixing, in the presence of a moisture-introducing plasticizer andof a substance selected'from the group consisting of the higher fattyacid esters, a 20% aqueous solution of gelatin acidulated with citricacid and about one part of a salt of an alkali metal and dichromic acidto four parts of the gelatin.

30. A coating for use in obtaining protection against attack bysubstances such as mustard gas, the coating being the product ofintermixing, in the presence of a moisture introducing plasticizer andof a substance selected from the group consisting of the higher fattyacid esters, a 20% aqueous solution of gelatin acidulated with citricacid and a salt of an alkali metal and dichromic acid, where theplasticizer is present in the ratio of about 10 to 40 parts ofplasticizer to 20 parts of gelatin and where about one part of hardeningagent is intermixed with four parts of gelatin.

31. The process of preparing protective shields against substances suchas mustard gasQincluding the steps of intermixing gelatin in aqueoussolution and a quantity of an oxidizing agent which also is effective asa hardening agent for gelatine, the quantit of such oxidizing agentbeing suflicient so that a substantial quantity thereof will remaineffective as an oxidizing agent and dispersed throughout the gelatinafter the gelatin has become hardened, and forming a protective film orlayer from the gelatin just before the hardening stage has beencompleted.

32. The process of preparing protective shields against substances suchas mustard gas, including the steps of intermixing gelatin in a weaklyacidulated aqueous solution together with a plasticizer and a quantityof an oxidizing agent which also is efiective as a hardening agent iorgelatine, the quantity of such oxidizing agent a being suificient sothat a substantial quantity thereof will remain efiective as anoxidizing agent and dispersed throughout the gelatin after the gelatinhas become hardened, and forming a protective film or layer from thegelatin just before the hardening stage has been completed.

33. The process of preparing protective shields against substances suchas mustard gas, including the steps of intermixing gelatin in a weaklyacidulated aqueous solution together with a plasticizer and a quantityof an oxidizing agent which also is effective as a hardening agent forgelatine at a substantially fixed temperature of 60 C., the quantity ofsuch oxidizing agent being suihcient so that a substantial quantitythereof will remain efiective as an oxidizing agent and dispersedthroughout the gelatin after the gelatin has become hardened, andforming a protective film or layer from the gelatin just before thehardening stage has been completed.

34. The process of preparing protective shields against substances suchas mustard gas, including the steps of intermixing gelatin in aqueoussolution weakly acidulated with citric acid together with a hygroscopicplasticizer and a quan tity of an oxidizing agent which also iseffective as a hardening agent for gelatine at a substantially fixedtemperature of 60 C., the quantity of such. oxidizing agent beingsufiicient so that a substantial quantity thereof will remain efiectiveasan oxidizing agent and dispersed throughout the gelatin after thegelatin has become hardened, and forming a protective film or layer fromthe gelatin just before the hardening stage has been completed.

35. The process of preparing protective shields against substances suchas mustard gas, including the steps of intermixing gelatin in a weaklyagainst substances such as mustard gas, includand being sumcient titythereof will remain aeeaeas v ing the steps of intermixing with a weaklyacid-' ulated 20% solution of gelatin a quantityior glycerin and asaltot dichromic' acid and an alkali metal at a substantially fixedtemperature of 60 0., the salt of dichromic acid being in the proportionof about one part to four parts of gelatin and being suflicient so thata substantial quantity thereof will remain effective asan oxidizingagent and dispersed throughout the gelatin atter the gelatin has becomehardened, and forming a. protective film or layer from the gelatin justbefore the hardening stage has been completed. i

37. The process of preparing protective.- shields against substancessuch as ulated 20% solution of gelatin a quantity of glycerin and a saltof dichromic acid and analkali metal at a substantially fixedtemperature of 60 0., the salt of dichromic acid being in the proportionof about one the gelatin has become hardened, the glycerin being in theproportion of about 10 to 40 parts to i about 20 parts of gelatin, andforming a protective film or layer from the hardening stage has beencompleted.

MAJER MENDEISOHN.

mustard gas, including the steps of intermixing with a weakly acid--part to four parts of gelatinso that a substantial quanefiective as anoxidizing s agent and dispersed throughout the gelatin after the gelatinjustbefore

